Materials Science Forum Vols. 532-533

Abstract: In order to improve the efficiency and quality in rough milling for open blisks, the plunge milling strategy is a good choice instead of the traditional 5-axis point milling and flank milling for deep and narrow channels machining. Theory and procedures of using a ruled surface to approximate a freeform surface are presented based on the theory of minimum area. The plunge milling strategy is discussed and developed for open blisks. And the NC programs of plunge milling is further developed and verified based on the UG software. At the end, the open blisk test piece was machined by plunge milling. The result reveals that high-speed plunge milling has increased efficiency greatly in the open blisks rough milling than the traditional methods.

Abstract: Tool monitoring is an important factor to restrict the improvement of production efficiency, machining quality and automation level. The monitoring of the tool wear and breakage conditions on YCM-V116B machining center was studied, and the acquired milling sound signals were analyzed in detail. By means of the classical time-frequency analysis, it was discovered that the wear sound had its own characteristic frequency band, and the frequency component within the frequency band would change according to the change of wear conditions. So that the frequency component within the frequency band will be a good indicator to monitor the tool wear conditions excellently. On the other hand, the tool breakage sound is a random signal that a transient change in amplitude is produced probably when tool breaks. The tool breakage conditions can be detected exactly by the advantages of wavelet decomposition techniques. The analysis implies that the sound generated during the machining process can be used to monitor tool conditions, which provides a new approach to the sound applications in tool monitoring domain.

Abstract: A new kind of Hydroxyapatite (HA) composites was fabricated using a hot-press method in which carbon nanotubes (CNTs) were introduced to the HA ceramic matrix to improve the mechanical properties of the resulting composites. The CNTs were treated using a mixture of nitric acid and sulfuric acid. A homogeneous dispersion of the CNTs in the HA matrix was achieved through dispersing them in the solution of surfactant. The bioactivity of the samples was tested. The microstructures of HA/CNT ceramic composites and the sample surfaces after immersion in SBF were characterized by SEM. The results showed that the introduction of the CNTs into HA ceramic matrix could produce positive strengthening effect without impairing the biological properties of the HA ceramic.

Abstract: Establishing a reasonable mechanical model for multi-pass conventional spinning and typical drawing spinning is the object of the present study. Research on stress and strain distribution during multi-pass conventional spinning processing under three modes of roller motion, i.e., one-way moving without profiling, one-way moving with profiling, and two-way moving with profiling, is carried out using elasto-plastic FEM method. Though the equivalent stress distribution under these three modes of roller motion is similar, there exists significant difference in magnitude, with the equivalent stress in the close-mandrel area being the highest in the case of profiled one-way moving. As far as the strain is concerned, it has a similar distribution as the equivalent stress, with the strain in the close-mandrel area under one-way moving with profiling having the highest value. In the case of roller two-way moving with profiling, the strain distribution is the most homogeneous, while the work-hardening of the blank is the most serious. In all cases, both stress and strain in the deforming zone increase with increasing spinning passes.

Abstract: A theoretical analysis on the variation regularity of cutting force caused by the material anisotropy with different orientation of KDP is analyzed firstly; influence and regularity of the variation are obtained. Analysis result shows that the crystal anisotropy of KDP is an important factor in obtaining the super-smooth surface. Then experiments are realized on the machine tool, results afford the variation regularity of cutting force caused by the anisotropy with different orientation of KDP, which certifies the correctness of this theoretical analysis. For ultra-precision machining of the KDP at large negative rake diamond cutter (-45°) and the optimal parameters, the super-smooth surface (rms is 8.702 nm, Ra is 6.895 nm) can be obtained on the plane (001).

Abstract: As machining technology develops toward the unmanned and automated system, the prediction of chip breaking is considered increasingly important, especially in continuous machining such as in cutting aluminum alloys. In this paper, chip breakers with different parameters are designed to produce chips that can be evacuated easily and reliably from the working zone. The formulation of chip up-curl radius is constructed through analyzing the chips subject to chip breaker. The predictive model of chip breaking is developed based on chip breaking conditions. Chip breaking strain is obtained by using backward-deducing method and cutting experiments. In order to verify the model, PCD tools with chip breakers are used to cut LY12, chip breaking areas are compared with those obtained from the predictive model. Results show the chip breaking predictive model is reasonable.

Abstract: Flame spray method was used to prepare the Al-Al2O3/TiO2 gradient coating on AZ91D magnesium alloy surface, where diffusion treatment for 2 hours at 380～420 °C was needed to reinforce the binding strength between the coating and the substrate. Appearance and compositions of the coating were analyzed by scanning electronic microscope (SEM) and electron probe microanalysis (EPMA), and the thermal shock resistance and wear resistance of the coating were tested. The result shows: Al-Mg diffusion is produced between the coating and the substrate, for good metallurgy; coating acquires high hardness and resistant to wear and thermal shock.

Abstract: The fabrication technology of microelectrode in electrochemical micromachining (EMM) was presented. The high frequency short pulses current and current density control between the cathode and anode were synthetically utilized. The mechanism of pulses EMM was expatiated firstly. The shaping principle of microelectrode was analyzed. The current density control strategy was proposed based on the fundamental experimental behavior of electrochemical machining current with the gap variance. Then an experimental setup for EMM is constructed, which has machining process detection and current density control functions, also a pulses power supply and a control computer are involved in. After the technologic experiment analyzed, some microelectrodes with nice surface are fabricated successfully. This method could provide the simple electrode for further electro-machining or micro probe for scanning probe microscopy. Preliminary experimental results show the feasibility of EMM and its potential capability for better machining accuracy and smaller machining size.

Abstract: This paper presents new machining technology of micro-EDM with lower working voltage in RC pulse power source. How to control the discharging energy of one pulse supplied by RC power is crucial to the technology of micro-EDM. The process of discharging has been studied, then the feasibility of machining with lower working voltage has been put forward, in order to reduce the discharge energy of one pulse effectively. On the basis of a great deal of experiments, the effect of working voltage on surface quality is studied, also the effect of working voltage on machining efficiency has been found out and been analyzed theoretically. The result shows that lower working voltage can reduce the working energy observably, and then improve the machining surface quality attended by reducing of machining efficiency. However, there is a good machining effect when the working voltage is about 15~20V. Considering working efficiency, a new technology of block electro-discharge grinding (BEDG) with lower working voltage has been applied. As shown by the experimental result with the technology, the minimum diameter of micro-shaft reaches 32m. Moreover, the micro-shaft has very high surface quality of Ra 0.1252m and its coaxial diameter error is controlled within 0.152m.

Abstract: Fatigue crack propagation is the chief style leading to the damage of engineering components. With the design change of modern engineering structure from conservative “safe-life” to “endurance/damage limit”, it brings new big contradiction. Bigger risk occurs when serving time of components extends to maximum. Regular NDT (Nondestructive Testing) methods cannot monitor the initiation and expansion process of short cracks inside components effectively. As an advanced NDT method, ICT (Industry Computed Tomography) has some particular advantages which regular NDT methods do not have. As a result, adopting the latest achievements on industry CT and fatigue fracture, this paper presented a new supervision method for short fatigue cracks propagation based on density field analysis. Experiments have proved that our proposed method could be a new way to inspect the components’ damage in service even to predict their life.